INTENSITY (Arb. Units) tOO 90 8C 70 60 50 40 30 (o) CONTROL DISTANCE (J•.m) 13 INTENSITY ( b ) (Arb. Units) 90 80 70 60 50 4C 343 INTENSITY (Arb. Units) 90 8O 70 60 5C 4O 30 HC RED 3, 5 rain DISTANCE (c) HC RED 3, 15rain I I I I I 20 :50 40 50 60 DISTANCE (d) ! INTENSITY (Arb. Units) 90- HC RED 5, I•0 rain 80- 40 so DISTANCE Figure 6. Cross-sectional intensity scans at 491 nm of hair fibers dyed with HC Red 3 from 50 vol.% aqueous ethanol dyebath at T = 42øC, pH 9.3, C = 5.0 g/l. (a) Undyed (control). (b) Dyed 5 min. (c) Dyed 15 min. (d) Dyed 120 min.

14 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS ABSORBANCE o.4ot- 0.30 0.20 O. tO HC RED 3, T =42•C C =5.0 g/l,15 min I I I 5.0 •0.0 15.0 20.0 25.0 DISTANCE FROM FIBER SURFACE (,u. rn) Figure 7. Dye concentration profile determined from Figure 6c. of HC Red 3 into human hair. It is evident that the observed pH effects are mainly due either to greater swelling of the hair fiber above pH 10 or to partial ionization of the dye molecule in lower pH ranges. The solvent effect must be associated with the lower solubility of HC Red 3 in aqueous solution, rather than in 50 volume percent Table V Diffusion Coefficients Calculated From Dye Concentration Profiles (HC Red 3, T = 42øC, pH = 9.5, C = 5.0 g/l, 50 vol.% aqueous ethanol) D(c) X 10 •ø Absorbance (cm2/s) O.O5 5.7 0.10 7.7 0.15 5.8 0.20 5.1 O.25 5.O 0.30 5.0 Average = 5.7